1. Field of the Invention
This invention is concerned with a method and apparatus which allows continuous, noncyclic refrigeration. In particular, the method and apparatus involves moving paramagnetic material, which is situate on the rim of a wheel, through a magnetic field. The paramagnetic material moves through the field, and heat is expelled into a hot thermal reservoir. As the paramagnetic material moves into an area containing the substance to be refrigerated or cooled, the magnetic field applied to the paramagnetic material is decreased, thus causing the material to cool. The magnetic field is tailored such that, as the paramagnetic material enters or comes in contact with the substance to be refrigerated, it is at the temperature of this substance. As it moves through the substance, either gas or liquid, the magnetic field is further decreased and the paramagnetic material continues to cool to slightly below the temperature of the substance being refrigerated, thus causing this substance to cool. When the paramagnetic material leaves the substance that is being refrigerated and again reenters the hot thermal reservoir area, the magnetic field is increased and the paramagnetic material heats up until it reaches the region of the most intense field, whereupon the paramagnetic material transfers the heat acquired from the substance that is being refrigerated and expels it into the hot thermal reservoir.
2. Description of the Prior Art
U.S. Pat. No. 3,413,814, J. R. Van Geuns, is directed to a method and apparatus for refrigeration in which the entropy of a paramagnetic substance is alternately varied by varying the external parameter such as a magnetic field and a fluid medium such as helium gas is flowed in alternate directions in heat exchanger relationship with the substance. During the directional flows, heat and cold are transferred from the substance to the fluid and corresponding to these flows there is a heat exchanger relationship, first by the portion of the fluid with an area absorbing heat from the fluid, and subsequently by a remote portion of the fluid with an area to be cooled. Fluid in the first area is at a generally higher temperature than fluid in the area to be cooled, and portions of fluid in the two areas are not intermixed. This invention is directed to a rotating wheel design and moves the working substance that is the paramagnetic material between the reservoirs, i.e., the hot thermal reservoir and the reservoir containing the substance to be cooled, while keeping all other parameters constant. The Van Geuns patent uses a regenerator and reverses the direction of gas flow, while the apparatus of this invention needs no regenerator, nor does it rely on heat exchangers to transfer heat from the medium to the respective reservoirs, nor does it require a directed flow of fluids. Applicants' method and apparatus are particularly concerned with the mass transport of medium directly through a porous working material.
U.S. Pat. No. 3,108,444, D. Kahn. The Kahn patent is directed to a refrigerator apparatus capable of producing temperature of the order of 4.degree. K. and is a magneto-caloric cryogenic refrigerator consisting of a pair of spaced, thermally isolated heat reservoirs, a material having superconducting properties moving between said reservoirs with said material being physically separated but in thermal contact with said reservoirs, subjecting a portion of this material to a magnetic field of critical field intensity, and effecting progressive relative movement between the material and the magnetic field to cause a net heat transfer from one reservoir to the other. The Kahn patent uses superconductors as the working material, whereas this invention uses a paramagnetic material. The use of superconductors as a working material causes limitations on the ability of the Kahn device to remove heat quickly. The reasons for this are that the entropy removable by a magnetic field per unit volume from the superconductors is 1 to 2 orders of magnitude smaller than from a paramagnet. Further, the rotation rate of the Kahn wheel using a superconductor is severely limited by eddy current and hysteresis losses. The apparatus of this invention uses an insulator as a working material and therefore the rotation rate of the wheel is not subject to the aforementioned limitation. Furthermore, the Kahn device and method does not shape the magnetic field so that it goes to zero in a graduated manner and therefore does not make use of the Carnot cycle, thus lowering its efficiency. In addition, the Kahn device separates the wheel from the high and low temperature reservoir by a metal membrane. This structure leads to poor heat transport between the working material and the reservoirs. In the device of the present invention the reservoir fluid saturates and travels through the porous working material that carries the heat away by means of mass transport. Thus, the device of this invention has of the order of 100 times more cooling power than the Kahn device.